Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Tone Junkie on December 30, 2010, 03:06:15 pm
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Ok maybe the correct way to ask is if I use, (please correct me if Im wrong) a full wave bridge rectifier does the doubling effect come at the cost of the Ma. powered.
Ok I was looking at the reverb power transformer at weber for a cheap experimental build it has 290 altogether with 100MA that would mean I would get 182volts after standard rectification under load, but if I could double that it would then be in the area of real use to me. And then if it does come at the expense halving the MA. usable to me would 50 Ma be enough for a firefly type build.Thanks Bill
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In a nut shell, yes. If you double the voltage, you half the current. P=IE P is a fixed rating of the power transformer. As voltage goes up, current goes down. That's the only trade off when using a voltage doubler. It's still full wave rectification. Maybe not a good idea for a zillion watt amp, but for the small stuff, it's a cost saver. Lookit just about every Silvertone. Cheap -n- works.
-Richard
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Which Weber PT are you talking about?
If you're talking about the WRVBPT used in the 5G15 reverb unit (or revibe unit), the secondary voltage is 260 and no center tap. That will put out 367v unloaded using a bridge. You can't use a conventional full wave recto with it, but you could use a single diode half wave recto.
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sluckey,
Thats unloaded, right? In the 5G15 (Fender 6G15), once loaded, would/does this trans. drop the extra 60/70 volts down to Fenders schemos listed 300 vdc at the rect. and choke junction? I always wonderd about that and why more co. did'nt offer a replacement for this schem with out the ct, for a FWB. Come to think of it ,does'nt Doug offer this trans for use with FWB? Does his once loaded in this schem end up at about at the Fender target vdc?
Thanks, Brad :smiley:
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Ya when looking at there specs it was confusing , thanks that is the one i will look in the section covering diode rectafication to see which rectifier set up your talking about. thanks Bill
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Now I cant find were i saw it before you wouldnt happen to have a link to the page showing a single diode half wave recto would you. sorry I searched but couldnt find it.
Bill
PS. my other computer that had all that type of info i would ever need crashed
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http://www.el34world.com/charts/CommonHookups.htm
It's in Doug's tube amp library, top of forum index page. You have to go down a little, you'll see it.
Brad :smiley:
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Which Weber PT are you talking about?
If you're talking about the WRVBPT
I used a modified tube bridge with mine....here's the drawing w/ voltages with 5Y3......5U4 or GZ34 will be slightly higher
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Geezer, how did you heat that 5Y3?
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Thats unloaded, right?
Yes. The voltage will drop depending on load current and PT internal resistance. Without knowing those, it's just a guess as to how much the voltage will drop.
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Geezer, how did you heat that 5Y3?
One of Doug's 5v/3A PT's
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Geezer, how did you heat that 5Y3?
It's in the --fine print-- at the bottom of his post's.....
Cunfuze-us say: "He who say "It can't be done" should stay out of him who doing it!" :laugh:
Brad :angel
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Ok maybe thats not the right cheap pt for cheap experimental build has anyone tried the weber wptgp transformer that looks as if it would be something Im familiar with the ht winding has a center tap which leaves me open to the standard diode rectifier setup Im used to.
Plus it has a 5 volt winding in case I would like to use a 5y3 or something else on top of that 150 MA is a good chunk of power with 5A on the heater windings. Enough talk Im ordering looks like a great cheap pt and I have some ot,s from other things Ive collected to make it even cheaper. The other transformer looked OK but by the time I were to buy a 5volt transformer it would kind of blow the extra low budget experiment.
With it I could also get 280 or 300 volts after the recto do i hear 6aq5,s anyone I have about 8 of them I won in some auctions a while back anyone know how many MA I need for a quad of those baby,s .
Sorry Im kind of running down a rabbit trail here.
Im such a dawg I have a great build close to finish and Im already daydreaming about the next.
Thanks Bill
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Ok maybe thats not the right cheap pt for cheap experimental build
I don't seem to remember any one saying that. Take it one step at a time. You can do a "firefly" build with the trans. you already have.
With that said.... What is it you want to build with the PT you already have?
You said you were wondering if the trans you had would work for a firefly build, the answer was yes it has the power to do that build. The rectifer set up is a different deal. So if your still wanting to do a firefly, you could/should look at the PT rectifer scehm (B+ vdc) as the next part of your build to figure out.
OTOH, a 6AQ5 SE and PP have been done here and at other sites many times with great success, but I'm not sure 50ma's will handel a PP, 6AQ5, but I could be wrong.
Hope this helps you, Brad :smiley:
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Brad i was looking at that transformer I didnt have it yet but I have money in my paypal account burning a whole in my pocket christmas was good . As i was thinking out loud you guys were kind of giving me ideas my first thought was to try a firefly build.
I have been meaning to do one for a while but then I went through my tube stash I want to use a tube other than 12au7 or similar there had been discussion about an ecc99 having great headroom for that type of build. But going through I have a bunch of 6aq5,s that I got with some other tubes I won. When I went back and looked they had this other cheap transformer at weber the numbers were wptgp for that transformer I should have opened a new topic and asked about that transformer. I know Tubnit has done a PP 6aq5 amp. My real focus was just to do a cheap build with an odd ball transformers.I havnt been lucky and got any old baldwin organs lately so I had to actually buy something. That transformer would do 6aq5 because after its been rectified I had a choice of 280 volts or several others up to 340volts it was kind of an oddball transformer but cheap and had a 150 MA. output with 5Amp on the heater tap enough for almost anything, and I new we wanted under 300volts for 6aq5 tubes.
For that Im sorry for both rambling on, Its late and for leading you guys down a rabbit trail. I sometimes like to think outloud here there are some great minds who are even more passionate about tube amps than I, having been bit by the bug long before me. I have several differant firefly schematics sitting on my wall one day hopefully soon I will build one. Thank You Brad for your help and especially telling me were the page on rectifier circuits was located and I look forward to chatting with you soon about another build. Thanks Bill
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Here's my single ended EL34/6L6 amp using the Weber tranny you're talking about. If it's plenty for this and Geezer's mini Bassman - it's plenty for a little Firefly. I didn't use a tube recto like Geezer which made things much easier.
I have it running the EL34 at the moment and when starting out w/ a 400r resistor @ ~16w Pd I got 337v under load condition. When I got it up to ~100mA/25w Pd it dropped down to 250v under that load condition. I'm getting the full (or very close) 11w RMS output from the EL34.
ps- I built a similar Firefly amp using the Hammond 190v tranny and it's plenty for that design and running all tubes 12au7, 12bh7, & ECC99 so the Weber @ 260v is more than enough (and w/out the voltage doubler). I run a 12bh7 mostly using a 470 Rk and this gives more volume & headroom and better overall sound and performance than a 12au7. The ECC99 JJ works well w/ even more of both but if you lower the Rk down to 220r or 250r you will get better performance out of that tube.
Here's the power section w/ VVR for my EL34 "Wildcat" build. You don't have to use the VVR part but can check out how to wire it w/ diodes (in case you don't know?). Also, I usually like to elevate my heaters on SE amps, I would suggest you do this for the Firefly & it's high gain nature.
Joe
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Thanks jojokeo that was nice of you to share that with me gives me many options.Bill